Molecular Structure, Quadrupole Coupling Tensor and Dipole Moment of Ethyl Cyanide

Abstract

The microwave spectra of CD3CH2CN, 13CH3CH2CN, CH3 13CH2CN and CH3CH2C15N have been measured. In addition the spectrum of CH3CH2 13CN has been remeasured with greater accuracy. From these spectra and those previously reported - CH3CH2CN, CH3CD2CN, CH2DCH2CN (sym) and CH2DCH2CN (asym) - a complete rs-structure has been calculated by the equations of Kraitchman and Chutjian. r0-structure calculations were performed with different assumptions due to the symmetry of the molecule. A comparison between r0- and rs-structure was made and showed good agreement especially for the atoms of the frame. The quadrupole coupling constants of the above mentioned isotopes of ethyl cyanide were obtained from the hyperfine structure of the spectra with the exception of CH3CH2C15N, which has no nucleus with quadrupole moment. The quadrupole coupling tensor in its principal axis system was determined from the constants of CD3CH2CN and CH3CD2CN using the angle e between their principal axes of inertia in the a-b-plane. From Stark effect measurements the dipole moment of CH3CH2CN was reevaluated. To determine the direction of the dipole moment Stark effect measurements for CD3CH2CN and CH3CD2CN were carried out.